Flies in general are a nuisance when flying around our kitchens, outdoors, and really just about anywhere they decide to hang out. It’s why we have the fly swatter. However, not all flies are born equal, and two species in particular are especially hated. If you’ve ever encountered a horse or deer fly, then you know why these horrid flying pests are so unpleasant to encounter. Both come from the family Tabadinae, and are a major nuisance pest to animals such as cattle and horses as well as humans. These guys don’t discriminate and are equal opportunity biters.

Horse and deer flies become a major problem in Massachusetts during the summer and early fall. They are active during the daytime, so the only sure way to avoid them is to only come out at night or never take a step outside during the day. Basically, you need to become a vampire. These flies are known for their painful bites that are so deep they will actually draw blood, as blood is exactly what they are looking to get. They use their mandibles and maxillae to penetrate the skin in a similar fashion to the way we use scissors to cut through paper. Their saliva contains anticoagulants that they pump into the wound so they can then ingest the blood with their sponging labella. Let’s just say, you don’t want one of these things biting you.

While they tend to feed on large animals like cattle and horses, they will happily consume human blood if it is available. People often see as many as 100 flies feeding on a single animal, and twenty to thirty flies feeding for as little as six hours are capable of consuming 100 cc of blood. Obviously, they aren’t really able to feed on humans in these numbers or for this amount of time because we are able to swat them away from us, unlike the poor cattle standing out in the sun with only their tail as a means of swatting them away. You can probably imagine that these flies are able to easily avoid being hit by an animal’s tail just by congregating farther up the body. This is why they tend to bite around the abdomen, legs, and neck.

We humans aren’t safe, however, as they have been known to bite a chunk out of us when given the chance. These rather sneaky flies are ambush predators. They will hide in shady areas, usually under bushes and trees, and wait for a tasty snack to walk by before they launch their surprise attack. They mostly use their sight to detect prey, watching for moving objects, particularly ones that are darker in color, but are also attracted to carbon dioxide and odor, much like mosquitos. This makes humans a pretty big target during the summer, as we stand out like a sore thumb in our colored clothing as we walk around outside, and the amount of carbon dioxide and strong odors we emit increase in the hot weather of summer. If you are doing anything outside, watch out for horse and deer flies that might be waiting just under the bushes to launch an attack.

Have you or someone you know ever been bitten by a horse or deer fly?